Corn ethanol and biodiesel can meet only a small fraction of what the U.S. needs for transportation fuels, Rice’s Kyriacos Zygourakis told an international gathering of energy analysts at the 2007 World Oil Conference Oct. 19 in Houston. The conference was sponsored by the Association for the Study of Peak Oil-USA.

Zygourakis, the A.J. Hartsook Professor of Chemical and Biomolecular Engineering, told the audience of several hundred that the weight of scientific evidence shows that corn ethanol — the U.S.’s major biofuel — takes more energy to produce than it provides and may pump more greenhouse gases into the atmosphere than the gasoline it replaces. He said other biofuels like biodiesel and cellulosic ethanol appear to be better bets, but early indications are that they may take up huge amounts of land to make a significant dent in replacing petroleum consumption.

KYRIACOS ZYGOURAKIS

“The picture for biofuels isn’t as rosy as some of the proponents would have us believe,” Zygourakis said. “There are major technical challenges ahead, and significant uncertainties still remain, particularly with regard to net energy production and greenhouse gas emissions.”

The term “peak oil” comes from a theory proposed by renowned Shell research geologist King Hubbert in 1949. Hubbert referred to “peak oil” as the point at which maximum global petroleum production would be reached. Following peak production, Hubbert predicted the rate of global oil production would enter terminal decline. Those who adhere to the theory don’t believe oil will suddenly run out, but they do believe supplies will drop and prices will increase after the peak.

Zygourakis’ speech — “How Good Is Our Bet on Biofuels?” — followed sobering talks by analysts who predicted that the global production of oil and natural gas could peak before 2015, that coal reserves will not last as long as some people believe and that there will not be enough uranium available to make nuclear energy a viable alternative. Several speakers at the conference noted that the price of a barrel of crude hit the $90 mark for the first time while the ASPO conference was going on.

Zygourakis told the audience that biofuels offered no silver bullet for the energy shortfall. He said data from several studies revealed that corn ethanol, in particular, was a poor alternative for gasoline. He said the 12 million U.S. acres dedicated to corn ethanol production in 2006 offset a scant 2.3 percent of the nation’s gasoline fuel demand for that year.

Evidence also suggests that corn ethanol actually requires more energy to produce than it provides, particularly when coal is used to power ethanol production plants or when corn is grown on marginal lands that have low yields but increased demands for irrigation and fertilizers.

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“That’s why the scientific community has focused its attention toward the so-called ‘second generation’ biofuels, and in particular on cellulosic ethanol,” Zygourakis said.

Unlike corn ethanol, which is produced from the starch in corn kernels, cellulosic ethanol is produced by converting the carbohydrates in the trunk, stalk and stems of plants into fuel. This allows a greater portion of the dry biomass of crops to be converted into fuel, particularly from “energy crops” like switchgrass or poplar.

However, there are still questions about how much net energy will be gained in the production of cellulosic ethanol. Zygourakis said estimates of cellulosic ethanol returning six to eight times the energy inputs are based on zero energy inputs at the processing plant. The thought is that all parts of the plant that cannot be converted to ethanol will be burned to power the refinery that produces the ethanol. But Zygourakis said that recent studies indicate that cellulosic biorefineries may require additional energy inputs.

“Based on these figures, it appears that more realistic estimates of the net energy ratio — the amount of energy returned per unit of energy put in — may be as low as 1.4,” Zygourakis said. “Literature data also suggest that the amounts of switchgrass collected from an acre of land may be significantly lower than the estimates used in some studies.”

Using more realistic figures for biomass and ethanol yields, Zygourakis estimated that even if 200 million acres of U.S. land — almost half the country’s total crop acreage or more than one-third of our grassland for pasture and range — were dedicated to switchgrass, the resulting ethanol would still supply less than 30 percent of the country’s 2005 gasoline usage.

Since “biorefineries,” the industrial plants where cellulosic ethanol will be produced, have yet to be built, the technology they ultimately employ will determine the viability of the nation’s biofuels production system.

“Providing the energy to power the biorefineries is where the battle is going to be won or lost,” Zygourakis said. “But even if we win this battle, we should not expect biofuels to become the long-term cure of our oil addiction.”

About Jade Boyd

Jade Boyd is science editor and associate director of news and media relations in Rice University's Office of Public Affairs.